The resolution of position coordinates of points, lines, segments, or regions of a plane surface has previously been accomplished by either a direct or indirect method. In the direct method, a measuring instrument such as a ruler or scale or protractor is used to measure length or angular coordinates relative to some fixed reference point. After, or in coincidence with the measurement, the measurement data may be recorded in a suitable data storage device. In the indirect method, a pointer is generally placed over the point on the plane surface whose position is to be resolved. In the process, analog signals corresponding to the coordinates of the point are produced. These analog signals are then conditioned for application to a computing and storage device where they are converted to numbers representing the position coordinates in a convenient coordinate system for the user.
The present invention falls under the general category of indirect methods of planar position coordinate resolution. The state-of-the-art in this category consists of the following two methods of coordinate resolution.
Method A--The image, picture, sketch, or graphical data upon which resolution of position coordinates is desired, is placed in close proximity to an insulated plane surface within which is imbedded a conductive grid network. This conductive network, when excited by a pair of differing types of electrical signals, produces orthogonal potential fields across its plane surface. A data take-off pen or pencil in contact with a given point of the image area whose position coordinates are desired transfers an electrical analog signal that is indicative of electric field potentials at the point and representative of its position coordinates to a computing and storage device, thus recording the location of that point.
Method B--A replica of the image, picture, sketch or graphical data is reflected, normally by use of a 45.degree. optical combining glass, onto the face of a cathode-ray display tube. A cursor is also displayed on the tube face. The coordinates of the cursor are controlled by a computing and storage device. The cursor is caused to trace, and rest upon successive points of the reflected data whose position coordinates are desired. At each point, the cursor coordinates are recorded by the computing and storage device.
Some of the major problems inherent in Methods A and B include the following.
Method A
(a) The conducting surface network and supporting circuitry is complex and expensive.
(b) Position coordinate computations must be performed using interpolation techniques since the conductor spacing is typically much wider than the desired image point-to-point resolution.
(c) Signal interference problems are possible due to the constant a-c power excitation applied to the conductive surface.
(d) The close proximity of the human hand may produce extraneous conductive paths and cause position errors to be introduced in the calculation.
Method B
(a) A precise and complex optical reflector is required to obtain a low-distortion replica of the desired image onto the curved surface of a cathode-ray tube.
(b) Reproduction errors are possible since position coordinates of the reflected image are obtained rather than those of the original image.
(c) The alignment of the cursor with the image element of interest on the display tube is difficult.
The solutions to the above listed problems are given in the DISCLOSURE OF INVENTION section.
A search of the prior art disclosed two patents Thompson and Heartz, that were directly related to the present invention. Three other patents indirectly related to the present invention were considered in the investigation and evaluation of the prior art. The cited patents are listed below:
______________________________________ PATENT NUMBER INVENTOR ISSUED ______________________________________ 2,538,226 Anderson et al 01/16/51 2,931,573 Story 04/05/60 3,106,707 Thompson 10/08/63 3,731,995 Reiffel 05/08/73 3,883,861 Heartz 05/13/75 ______________________________________
The Anderson patent describes an analog computing means for solving vector triangles. The Story patent discloses an apparatus which is capable of transforming rectangular coordinates into polar coordinates, or for solving problems which are analogous to such transformation. The Thompson patent discloses an apparatus for transforming planar image data into electrical analog signals using an electrically conductive transparent material and an electrically conductive data take-off pencil. The Reiffel patent incorporates the Thompson invention into an electrical-optical system for producing animated motion pictures. The Heartz patent discloses an apparatus for encoding in digital format and simultaneously displaying a data base descriptive of a land mass or the like. The information being encoded is simultaneously displayed, and compared with the source of the information, which may be a map or photograph.